Liquid crystal display device

ABSTRACT

Antiferroelectric liquid crystal display device provided with a selection period tw, during which a scanning voltage is applied for determining a liquid-crystal display condition or state of a pixel, and further provided with a holding period tk, during which the determined liquid-crystal display state of the pixel is held, and a relaxation period ts, in which the state of the liquid crystal is changed from a ferroelectric state to an antiferroelectric state before the selection period tw and after the holding time tk. Moreover, in the case of this device, at least one horizontal scanning interval, in which the scanning signal voltage is not zero at least during a display signal active period, is provided in the relaxation period ts.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display device usingan antiferroelectric liquid crystal display panel that has a pluralityof column electrodes and a plurality of row electrodes.

BACKGROUND ART OF THE INVENTION

An antiferroelectric liquid crystal is stable in an antiferroelectricphase or state when left in a condition that no voltage is applied tothe liquid crystal (namely, the voltage to be applied to the crystal(substance) is zero). Hereinafter, this stable state will be referred toas a neutral state. An antiferroelectric liquid crystal panel may beconfigured in such a manner as to effect either a dark display or abright display in this neutral state. Although antiferroelectric liquidcrystal panels of the present invention be applied to both a darkdisplay and a bright display, an antiferroelectric liquid crystal panelof the present invention which is adapted to effect a dark display inthe neutral state will be described hereinbelow.

FIG. 16 is an example of a graph illustrating the optical transmittanceof an antiferroelectric liquid crystal relative to a voltage appliedthereto. In this graph, the abscissa represent the applied voltage; andthe ordinate the optical transmittance.

When applying a positive voltage to the crystal, which has been in theneutral state at a point 0, and increasing the positive voltage, thetransmittance abruptly increases at a voltage Ft. Then, thetransmittance reaches nearly the maximum value at a voltage Fs.Consequently, the crystal is put into a saturated ferroelectric state.Thence, the optical transmittance does not change much even when ahigher voltage is applied thereto. Next, when the applied voltage isgradually decreased, the optical transmittance abruptly drops at avoltage At. Further, the transmittance nearly reaches zero at thevoltage As. Thus, the crystal returns to an antiferroelectric state.Similarly, if a negative voltage is applied to the crystal when theapplied voltage is 0 V, and the applied negative voltage is made morenegative, the transmittance abruptly rises at a voltage (-Ft). Then, thetransmittance nearly reaches the maximum value at a voltage (-Fs). Thusthe crystal is put into a saturated ferrorelectric state. Thence, whengradually the applied negative voltage is reduced to 0 V, thetransmittance abruptly drops at a voltage (-At). Further, thetransmittance becomes almost zero at a voltage (-As). Thus, the crystalreturns to the antiferroelectric state. As above described, there aretwo causes for a ferroelectric state of the liquid crystal. Namely, oneis the application of the positive voltage, and the other is theapplication of the negative voltage. Hereunder, the ferroelectric statedue to the former cause will be referred to as (+) ferroelectric state,while the ferroelectric state due to the latter cause will be referredto as (-) ferroelectric state. Further, |Ft| designates a ferroelectricthreshold voltage; |Fs| a ferroelectric saturation voltage; |At|designates an antiferroelectric threshold voltage; and |As| anantiferroelectric saturation voltage.

Generally, it is often the case that the curves (namely, the hysteresiscurves) of FIG. 16 representing the optical transmittancecharacteristics of a liquid crystal relative to the voltage appliedthereto are obtained by applying thereto a triangular-wave-like voltagewhich is generated in such a manner that the absolute value of the ratioof a change in this voltage relative to time, namely, the value of|dV/dt| is constant. However, in this case, if the value of |dV/dt| ischanged, the shapes of the hysteresis curves also change. Moreover, thevalues of the aforementioned quantities As, Ft, Fs and At also vary. Itis, accordingly, necessary to specify these values to specify theaforesaid value of |dV/dt|. However, in the case of the device of thepresent invention, data concerning the graph of FIG. 16 is obtained bythe following method so as to obtain values of quantities correspondingto actual driving conditions. In this case, it is assumed that thetemperature thereof is the working temperature.

Moreover, it is further assumed that the duration of one frame (to bedescribed later) is Pt and that the length of a time period in which aselection voltage (to be described later) is applied to an liquidcrystal, is Wt.

(1) A pulse voltage, whose duration is Wt and voltage level is Vz, isapplied to the liquid crystal that is in a stable antiferroelectricstate (namely, in the neutral state). Further, the relationship betweenthe optical transmittance and the pulse voltage Vz at the time ofcompletion of the application of this pulse voltage is plotted.Moreover, this operation is repeated by changing the value of thevoltage Vz. Thereby, the curve drawn from the point O to thetransmittance corresponding to the voltage Fs through the transmittancecorresponding to the voltage Ft of FIG. 16, as well as the curve drawnfrom the point O to the transmittance corresponding to the voltage (-Fs)through the transmittance corresponding to the voltage (-Ft), isobtained.

(2) Next, the liquid crystal is first put into the saturatedferroelectric state by applying thereto a voltage which is not lowerthan the aforementioned voltage |Fs|. Then, at a moment 0, the appliedvoltage is reduced to |Vz|. Thence, after the elapse of the time periodof the length (Pt-Wt), the relation between the optical transmittanceand the applied voltage Vz is plotted. Moreover, this operation isrepeated by changing the value of the voltage |Vz|. Thereby, the curvedrawn from the transmittance corresponding to the voltage Fs to thepoint O through the transmittances respectively corresponding to thevoltages At and As of FIG. 16, as well as the curve drawn from thetransmittance corresponding to the voltage (-Fs) to the point O throughthe transmittances respectively corresponding to the voltages (-At) and(-As), is obtained.

When some liquid crystal panels are used, the curve (namely, the curvedrawn from the transmittance corresponding to the voltage Fs or (-Fs) tothe point O in FIG. 16) obtained in the aforementioned case (2)sometimes intersects the ordinate axis. The main cause of this is theresponsivity of the liquid crystal. Namely, in the case that the liquidcrystal is maintained in the ferroelectric state by applying thereto avoltage, which is not lower than the aforementioned voltage |Fs|, andthat at the moment 0, the applied voltage Vz is changed into 0, theliquid crystal finally becomes stable in the antiferroelectric stateafter the elapse of a certain time period (hereunder referred to as arelaxation time tn). However, if this relaxation time tn is longer thanthe time period (Pt-Wt), the curve obtained in the aforementioned case(2) intersects with the axis of ordinate.

When actually driven, it is difficult to bring such a liquid crystalpanel into a completely antiferroelectric state. It is, thus, consideredthat in the case of such a liquid crystal panel, a dark display cannotbe effected and that the contrast is extremely degraded.

Generally, a liquid crystal panel is driven by performing the followingprocess. Namely, first, N row electrodes and M column electrodes areformed in such a manner as to be arranged as a matrix of N rows and Mcolumns. Further, a scanning signal is applied to each of the rowelectrodes through a row-electrode drive circuit, while a display signaldepending on display data representing each pixel (incidentally, a partof data represented by the display signal is sometimes not dependent onthe display data) is applied to each of the column electrodes through acolumn-electrode drive circuit. Moreover, a voltage (hereunder referredto simply as a synthesis voltage), which corresponds to the differencebetween the scanning signal and the display signal, is applied to aliquid crystal layer. Thus, the liquid crystal panel is driven. The timeperiod required to scan all of the row electrodes (namely, 1 verticalscanning interval) is usually referred to as 1 frame (or 1 field). Inthe case of driving the liquid crystal panel, the polarity of a drivingvoltage is reversed or inverted each frame (or every frames) in order toprevent the liquid crystal from being adversely affected (namely,prevent the degradation of the liquid crystal due to a non-uniformdistribution of ions).

Paying attention to the scanning signal to be applied to a single rowelectrode, 1 vertical scanning interval is composed of N horizontalscanning intervals (in some case, an additional interval is addedthereto). Among a horizontal scanning interval, a part of horizontalscanning interval in which a scanning voltage (hereunder referred to asthe selection voltage) to be used for determining the display conditionof a pixel on this row is applied, is referred to as a selection periodtw. The other part of horizontal scanning interval are referred to asnon-selection periods.

FIG. 17 illustrates the waveforms of signals flowing through the rowelectrodes, the column electrodes and the pixel synthesis electrodes ofa liquid crystal panel in which the N row electrodes and the M columnelectrodes are formed in such a manner as to be arranged as a matrix ofN rows and M columns. The display conditions or states of pixels areassumed to be as follows. Namely, in the case of a first column (Y1),pixels respectively corresponding to intersections with all rows aredisplayed in white. Further, in the case of a second column (Y2), apixel corresponding to an intersection with a first row is displayed inblack. Pixels respectively corresponding to intersections with the otherrows are displayed in white. Moreover, in the case of pixels in a thirdcolumn (Y3), these pixels respectively corresponding to intersectionswith all rows are displayed alternately in black and in white.Furthermore, in the case of an Mth column YM, pixels respectivelycorresponding to intersections with all rows are in a black displaystate, namely, displayed in black.

Scanning signals are respectively applied to the N row electrodes insequence from the top row to the bottom row so that the waveforms of thescanning signals respectively corresponding to the adjacent rowelectrodes are shifted by a phase corresponding to a time that is (1/N)of the frame interval. Display signals are respectively applied to the Mcolumn electrodes so that the waveform of the display signal applied toeach of the column electrodes is synchronized with that of the scanningsignal applied thereto and is generated according to the displayconditions of the pixels corresponding thereto, namely, according towhether the pixels are displayed in white or in black.

Turning to a synthesis voltage corresponding to each pixel, the voltageapplied to a pixel P11, which is displayed in white in a first row, inthe selection period tw is large, whereas the voltage applied to a pixelP12, which is displayed in black in the first row, in the period tw issmall. The other part of the synthesis voltage has the same waveform.The synthesis voltage applied to a pixel P21, which is displayed inwhite in a second row, has a waveform which is almost the same as thatobtained by shifting the waveform of the synthesis voltage applied tothe pixel P11 by the phase corresponding to a time period that is (1/N)of the frame interval. Here, note that the first frame and second framein the first row and second row are shifted each other by (1/N).

Usually, in the case of the antiferroelectric liquid crystal panel, itis determined on the basis of the aforementioned display signal at thetime of applying the selection voltage whether the state of the liquidcrystal, which has been in the antiferroelectric state, is maintained oris changed into the ferroelectric state. Thus, there is the necessity ofa time period (hereunder referred to as a relaxation period ts) requiredfor setting the liquid crystals in the antiferroelectric state beforethe application of the selection voltage. During a time period which isother than the selection period tw and the relaxation period ts, thedetermined state of the liquid crystal should be held. Hereunder, thistime period will be referred to as a holding or keeping period tk.

Further, there are two kinds of known driving systems, namely, a systemin which the aforementioned relaxation period ts is provided in theaforesaid selection period tw (see, for example, Japanese UnexaminedPatent Publication (Kokai) No. 4-362990/1992), and another system inwhich the aforementioned relaxation period ts is provided in a timeperiod (namely, the non-selection period) that is other than theaforesaid selection period tw (see, for instance, Japanese UnexaminedPatent Publication (Kokai) No. 6-214215/1994).

FIG. 18 illustrates the waveforms of a scanning signal Pa applied to agiven pixel of interest, display signals Pb and Pb', synthetic signalsPc and Pc' and optical transmittances L100 and L0 according to thedriving method described in FIGS. 1 and 2 of the aforementioned JapaneseUnexamined Patent Publication (Kokai) No. 4-362990/1992.

In FIG. 18, reference characters F1 and F2 designate the first frame andthe second frame, respectively. This figure illustrates the case wherethe polarity of the aforementioned driving voltage is reversed everyframe. As is apparent from this figure, the first frame F1 is differentfrom the second frame F2 only in that the polarity of the drivingvoltage is inverted. As is obvious from the aforementioned FIG. 16, theoperation of the liquid crystal display device is symmetrical withrespect to the polarity of the driving voltage. Therefore, the followingdescription will be given regarding only the first frame, unlessdescriptions concerning the second frame are necessary. Further, thedescription concerning the second frame, which is different from thefirst frame only in the polarity of the applied voltage, is omittedherein.

Further, in the following description and drawings of the waveform ofdriving signals, the electric potential indicated as "0" does not meanabsolute electric potential but means mere reference electric potential.Therefore, in the case that the reference electric potential varies forsome reason, scanning signals and display signals vary relatively.Moreover, in the case that the word "voltage" is used in connection withthe scanning signals and the display signals in the followingdescription, the word "voltage" designates the difference between theelectric potential indicated by such a signal and the reference electricpotential.

As shown in FIG. 18, 1 frame is divided into three time periods, namely,the selection period tw, the holding period tk and the relaxation periodts. The selection period tw is further divided into time periods tw1 andtw2, which have equal lengths. The voltage level of a scanning signal Pain the first frame F1 is set as follows. Needless to say, in the secondframe F2, the polarity of the voltage is inverted. Here, note that ±Vdesignates the selection voltage and that the length of the time periodtw2 corresponds to the duration Wt of the pulse voltage.

    ______________________________________                                        Time Period     tw1    tw2      tk   ts                                       ______________________________________                                        Scanning Signal Voltage                                                                       0      +V1      +V3  0                                        ______________________________________                                    

Further, the display signal is set as follows. Here, note that thesymbol "*" indicates that the voltage depends on the display datarepresenting other pixels in a same column as this pixel.

    ______________________________________                                        Time Period        tw1    tw2      tk  ts                                     ______________________________________                                        On-State Display Signal Voltage                                                                  +V2    -V2      *   *                                      Off-State Display Signal Voltage                                                                 -V2    +V2      *   *                                      ______________________________________                                    

In the case of the hysteresis curves of FIG. 16, generally, the curvedrawn from the transmittance corresponding to the voltage As to thetransmittance corresponding to the voltage Ft or from the transmittancecorresponding to the voltage At to the transmittance corresponding tothe voltage Fs is not flat. Thus, when the voltage applied to the liquidcrystal in the holding period tk is shifted depending on the displaysignal, a change in the brightness in this holding period is caused. Toprevent an occurrence of this phenomenon, usually, the polarity of thedisplay signal is inverted in such a manner that the average valuethereof in a horizontal scanning interval is 0. Namely, the time periodtw1 is different from the time period tw2 in that the polarity of thedisplay signal is inverted. Hereunder, a time period, in which a displaysignal should be applied thereto according to the display data(incidentally, the waveform of the signal varies with the display data)in all of the time periods (namely, the selection period, the holdingperiod and the relaxation period) will be referred to as a displaysignal active period. For example, in the case of FIG. 18, one period orcycle of the display signal Pb consists of a time period, in which thissignal has a signal level of +V2, and another time period in which thissignal has a signal level of (-V2). Thus, the signal voltage of +V2 or(-V2) is applied thereto at all times, so that all of the time periodsare the display signal active period. However, in the case of FIG. 19 aswill be described in detail later, the period or cycle of the displaysignal Pb consists of a time period, in which the signal voltage is 0,and another time period, in which this signal has a signal level of +V2,and still another time period in which this signal has a signal level of(-V2). Thus, the time period in which the display signal is appliedthereto is those in which the signal voltages of +V2 and (-V2) otherthan 0 are applied thereto. Consequently, these time periods are thedisplay signal active period in this case.

In FIG. 18, reference characters Pb, Pc and L100 respectively denote thewaveform of a display signal, that of a synthetic signal and opticaltransmittance in the case that all of the pixels provided on a columnelectrode, to which a pixel of interest belongs, are in an on-state(namely, in a bright or light state). In this case, if the (synthetic)voltage to be applied to the liquid crystal in the time period tw2 meetsthe following condition: |V1+V2|>|Fs| (see FIG. 16), the transition ofthe state of the liquid crystal into the ferroelectric state is started.As a result, the optical transmittance of the liquid crystal increases.In the holding period tk, if the following condition is satisfied:|V3-V2>|>|At|, the bright state is held. In the relaxation period ts, ifthe following condition is satisfied: |V2 |<|As|, the transmittancedecreases with the elapse of time. Thus, the relaxation of the liquidcrystal, namely, the change of the state thereof from the ferroelectricstate to the stable antiferroelectric state is attained.

Further, in FIG. 18, reference characters Pb', Pc'and L0 respectivelydesignate the waveform of a display signal, that of a synthetic signaland optical transmittance in the case that all of the pixels provided ona column electrode, to which a pixel of interest belongs, are in anoff-state (namely, in a dark state). In this case, if the syntheticvoltage to be applied to the liquid crystal in the time period tw2 meetsthe following condition: |V1-V2|<|Ft|, the voltage applied in theholding period tk meets the following condition: |V3+V2|<|Ft|, and thevoltage applied in the relaxation period ts meets the followingcondition: |V2|<|Ft|, the dark state is held.

FIG. 19 is a waveform diagram illustrating the waveform of a drivingsignal used in the driving method that is described in JapaneseUnexamined Patent Publication (Kokai) No. 6-214215/1994. In the case ofthis driving method, 1 frame is divided into the selection period tw andthe holding period tk. The selection period tw is further divided intothree time periods, namely, two time periods tw1 and tw2, which haveequal lengths, and a time period two which precedes the two periods tw1and tw2. In the case of this driving method, the aforementionedrelaxation period ts is the aforesaid time period tw0. Further, thevoltage level of a scanning signal and the display signals in the firstframe F1 are set as follows.

    ______________________________________                                        Time Period      tw0    tw1      tw2  tk                                      ______________________________________                                        Scanning Signal Voltage                                                                        0      0        +V1  +V3                                     On-State Display Signal Voltage                                                                0      +V2      -V2  *                                       Off-State Display Signal Voltage                                                               0      -V2      +V2  *                                       ______________________________________                                    

In the case of the driving method described in Japanese UnexaminedPatent Publication (Kokai) No. 6-214215/1994, the zero-volt voltageapplying time period (tw0) provided in the leading part of the selectionperiod tw is used as the relaxation period ts. In this case, a timeperiod having the length (tw-tw0), namely, a part of the period tw,which is other than the time period tw0 during when the display signalvoltage is 0, is the display signal active period. In the case of thisdriving method, when using a liquid crystal panel whose relaxation timetn is long, the state thereof cannot be changed into theantiferroelectric state unless the length of the period tw0 issufficiently increased. Hence, the panel cannot help but increase thelength of the selection period tw (namely, 1 horizontal scanninginterval). Thus, in the case of a highly fine display device (whosehorizontal scanning interval is short if the frame frequency isconstant), inconveniences are caused.

Regarding this respect, in the case of the driving method illustrated inFIGS. 1 and 2 of Japanese Unexamined Patent Publication (Kokai) No.4-362990/1992, a plurality of horizontal scanning intervals in thenonselection period are utilized as the relaxation period ts. Thus, evenif the relaxation period tn of the liquid crystal panel is large, thereis no necessity of increasing the length of the selection period tw.However, the optical transmittance of a liquid crystal in the relaxationperiod ts does not reflect display data correctly. Further, the opticaltransmittance thereof is unstable toward a change in temperature.Therefore, if the ratio of the relaxation period ts to one frame islarge, a favorable display cannot be obtained. For instance, in the casethat a time period corresponding to 1 pixel (namely, a total of thelengths of the selection period, the holding time and the relaxationtime) in 1 frame is 20 msec, and if the relaxation time should be atleast 18 msec, 90% of the length of 1 frame is occupied by an unstabledisplay time. Consequently, it becomes difficult to obtain a favorabledisplay.

SUMMARY OF THE INVENTION

Accordingly, problems to be resolved by the present invention are toreduce the length of the aforementioned relaxation period ts by a noveldriving method and to provide an antiferroelectric liquid crystaldisplay device, which can provide a preferable display even in the caseof using a liquid crystal panel, whose relaxation time tn is long, andfurther to provide an antiferroelectric liquid crystal display device,whose performance is higher, by extending the range of choice of aliquid crystal panel.

Japanese Unexamined Patent Publication (Kokai) No. 4-362990/1992describes that in the case where the antiferroelectric liquid crystal isin the ferroelectric state or phase and a voltage, whose absolute valueis not less than |At| and polarity is inverted, is applied thereto, ifthe ferroelectric state is the (+) ferroelectric state, the liquidcrystal is easily changed into the (-) ferroelectric state.Alternatively, in such a case, if the ferroelectric state is the (-)ferroelectric state, the liquid crystal is easily changed into the (+)ferroelectric state. According to this, "in the case that a voltage,whose absolute value |V| meets the following condition: |At|<|V|<|Ft|,is applied to a liquid crystal, which has been in the ferroelectricstate, by periodically inverting the polarity of the voltage every timeperiod (t), the transition of the state of the liquid crystal isperformed between the (+) ferroelectric state and the (-) ferroelectricstate every inversion of the polarity of the applied voltage. Thus, theliquid crystal is not stabilized into the antiferroelectric state".

FIG. 20 is a diagram obtained by re-drawing Pa, Pb, Pc and L100 of FIG.18 paying attention especially to the relaxation period ts. In therelaxation period ts, a group of voltage pulses, whose absolute value isnot more than the antiferroelectric threshold voltage (As), are applied.

However, according to investigations or researches on this by theinventor of the present invention, the behavior of the liquid crystaldepends upon the relaxation time tn, a voltage application time (namely,a time period during which the voltage is applied) t, and the magnitudeof the voltage |V|. Further, the inventor of the present invention hasdiscovered the fact that in the case of some values of tn, t and |V|,the liquid crystal is sometimes brought into the antiferroelectric statewithout maintaining the ferroelectric state even if the applied voltagesatisfies the aforementioned condition: |V|>|At|. Furthermore, theinventor of the present invention has discovered the fact that the timerequired for achieving the relaxation in the case, in which the absolutevalue of the voltage meets the condition: |Ft|>|V|>|As|, is shorter thanthe time required in the case, in which the absolute value of thevoltage meets the condition: |V|<|As|. In addition, the inventor of thepresent invention has discovered the fact that in the process of thetransition of the state of a liquid crystal from the ferroelectric stateto the antiferroelectric state, the optical responses of the liquidcrystal contain relatively quick responses and relatively slow response.To solve the problems by utilizing such properties of liquid crystals,the liquid crystal display device of the present invention, which isprovided with a selection period tw, a holding period tk and arelaxation period ts after the holding period tk and before theselection period tw for performing the relaxation of the state of theliquid crystal from the ferroelectric state to the antiferroelectricstate, uses the following means.

The first means used by the device of the present invention for solvingthe aforesaid problems is to set the absolute value of a display signalvoltage |V2| at a value which is larger than the absolute value of theantiferroelectric saturation voltage |As| (see FIG. 1).

The second means used by the device of the present invention for solvingthe aforesaid problems is to establish at least one horizontal scanninginterval, in which the scanning signal voltage is not zero at least in adisplay signal active period, in the relaxation period ts (see FIG. 2,FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 10, FIG. 12, FIG.13 and FIG. 15).

The third means used by the device of the present invention for solvingthe aforesaid problems is to establish at least tw0 horizontal scanningintervals, in which the scanning signal voltage is not zero at leasthalf of the display signal active period in one cycle or period of adisplay signal, in the relaxation period ts (see FIG. 14).

The fourth means used by the device of the present invention for solvingthe aforesaid problems is to establish both of a horizontal scanninginterval, in which the aforementioned non-zero scanning signal voltageis positive, and another horizontal scanning interval, in which thescanning signal voltage is negative, in addition to the second or thirdmeans (see FIG. 4, FIG. 12, FIG. 13, FIG. 14 and FIG. 15).

The fifth means used by the device of the present invention for solvingthe aforesaid problems is to provide the scanning signal voltage from analternating variation voltage source at least in a part of therelaxation period ts, in addition to the second or third means (see FIG.13, FIG. 14 and FIG. 15).

The sixth means used by the device of the present invention for solvingthe aforesaid problems is to make the voltage from the alternatingvariation voltage source zero in a part of each of the horizontalscanning intervals, in addition to the fifth means (see FIG. 14 and FIG.15).

The seventh means used by the device of the present invention forsolving the aforesaid problems is to make the scanning signal voltagechange in response to variation in temperature at least in a part ofeach of the relaxation period ts, in addition to the second or thirdmeans (see FIG. 10 and FIG. 11).

The eighth means used by the device of the present invention for solvingthe aforesaid problems is to set the scanning signal voltage as aselection voltage in a first half of a display signal active period inone cycle or period of a display signal and to set the scanning signalvoltage as being equal to a scanning signal voltage, which isestablished in the holding period tk, in a second half of the displaysignal active period, in addition to the second or third means (see FIG.8 and FIG. 15).

The ninth means used by the device of the present invention for solvingthe aforesaid problems is to set the absolute value of a scanning signalvoltage at a value which is equal to the absolute value of a scanningsignal voltage established in the holding period tk, in at least a partof relaxation period ts in addition to the second or third means (seeFIG. 3).

The tenth means used by the device of the present invention for solvingthe aforesaid problems is to set a first non-zero scanning signalvoltage in the relaxation period ts at a negative voltage when the stateof the liquid crystal in a precedent holding period is a (+)ferroelectric state, and at a positive voltage when the state of theliquid crystal in the precedent holding period is a (-) ferroelectricstate, in addition to the second or third means (see FIG. 2, FIG. 3,FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 and FIG. 12).

The eleventh means used by the device of the present invention forsolving the aforesaid problems is to apply to a liquid crystal a voltagewhich is greater than an antiferroelectric saturation voltage and issmaller than a ferroelectric threshold voltage, in a time period inwhich a scanning signal voltage is not zero, in the relaxation periodts, in addition to the second or third means.

The twelfth means used by the device of the present invention forsolving the aforesaid problems is to periodically invert the polarity ofa scanning signal voltage to be applied in the relaxation period ts, inaddition to the second or third means (see FIG. 12, FIG. 13, FIG. 14 andFIG. 15).

By using the aforementioned means, the liquid crystal having been in theferroelectric state is stabilized into the antiferroelectric state in arelatively short time without continuously establishing time periods inwhich a voltage being not more than an antiferroelectric saturationvoltage set in a hysteresis curve is applied. Moreover, constraintsplaced on liquid crystal panels are eased, so that various liquidcrystal panels can be selected. Consequently, an optimum display deviceis provided.

ADVANTAGES OF THE INVENTION

In accordance with the present invention, even in the case that theliquid crystal panel has a long relaxation time tn, there is provided anantiferroelectric liquid crystal display device being capable ofeffecting a favorable display. Moreover, constraints having beenhitherto placed on antiferroelectric liquid crystal panels aremitigated. Thereby, the kinds of available antiferroelectric materialsare increased. Furthermore, the production of the antiferroelectricliquid crystal display device is facilitated without heavily burdeningthe drive circuit and the panel structure. In addition, there isprovided an antiferroelectric liquid crystal display device, whosedisplay quality is not degraded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a first embodiment of the presentinvention;

FIG. 2 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a second embodiment of the presentinvention;

FIG. 3(a) is a diagram illustrating the driving waveforms and theoptical transmittance in the case of a third embodiment of the presentinvention;

FIG. 3(b) is a diagram illustrating the driving waveforms and theoptical transmittance in the case that a selection voltage is applied ina first half of the selection period in the third embodiment of thepresent invention;

FIG. 4 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a fourth embodiment of the presentinvention;

FIG. 5 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a fifth embodiment of the presentinvention;

FIG. 6 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a sixth embodiment of the presentinvention;

FIG. 7 is a diagram illustrating the driving waveforms in the case of aseventh embodiment of the present invention;

FIG. 8 is a diagram illustrating the driving waveforms in the case of aneighth embodiment of the present invention;

FIG. 9 is a diagram showing the driving waveforms and the opticaltransmittances in the case of the device of the present invention, whichillustrates the influence of temperature thereon;

FIGS. 10(a)-10 (c) are diagrams showing the waveforms of scanningsignals used in the ninth embodiment; FIG. 10(a) illustrates the casewhere the scanning signal voltage is changed depending on temperature ina forced relaxation period; FIG. 10(b) illustrates the case where bothof the scanning signal voltage in a forced relaxation period and thescanning signal voltage in a damping or decelerating relaxation periodare changed in such a manner as to depend on temperature; and FIG. 10(c)illustrates the case where only the scanning signal voltage in thedamping or decelerating relaxation period is changed in such a way as todepend on temperature;

FIG. 11(a) is a block diagram illustrating the circuit configuration ofa ninth embodiment of the present invention; and

FIGS. 11(b) to 11(e) are characteristic diagram illustrating the mannerof temperature compensation;

FIG. 12 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a tenth embodiment of the presentinvention;

FIG. 13 is a diagram illustrating the waveforms of the scanning signaland those of variation or varying voltage signals in the cases ofeleventh and twelfth embodiments of the present invention;

FIG. 14 is a diagram illustrating the waveforms of the scanning signalsand those of alternating (variation) voltage signals in the case of athirteenth embodiment of the present invention;

FIG. 15 is a diagram illustrating the waveforms of the scanning signalsand those of alternating voltage signals in the case of a fourteenthembodiment of the present invention;

FIG. 16 is a diagram illustrating change in optical transmittancerelative to voltages applied to an antiferroelectric liquid crystalpanel;

FIG. 17 is a diagram illustrating the waveforms of the signals flowingthrough the row electrodes, the column electrodes and the pixelsynthesis electrodes of the liquid crystal panel in which the N rowelectrodes and the M column electrodes are formed in such a manner as tobe arranged like a matrix of N rows and M columns;

FIG. 18 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of a conventional driving method;

FIG. 19 is a diagram illustrating the driving waveforms in the case ofthe conventional driving method; and

FIG. 20 is a diagram illustrating the driving waveforms and the opticaltransmittance in the case of another conventional driving method.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the embodiments of the present invention will be describedin detail by referring to the accompanying drawings. Incidentally, inthe drawings to be referred to in the following description, regardingthe time axis or base, the length of a time period is scaled in a mannersimilar to the way of scaling in the case of the conventional deviceillustrated in FIG. 20. Namely, in the drawings, the relaxation periodts is illustrated as being longer than the holding period tk. However,the holding period tk is actually longer than the relaxation period ts.Further, similarly as in the case of the aforementioned conventionalcase, the following description will be given regarding only the firstframe, unless descriptions concerning the second frame are necessary.

Incidentally, in the case of each embodiment of the present invention,the waveforms illustrated in the drawings are obtained in the case wherethe present invention is performed on the antiferroelectric liquidcrystal panel provided with the relaxation period tn, which does notmake a transition of the state to the antiferroelectric state unless therelaxation period ts is set in such a manner as to be equal to or longerthan 18 ms in the case that the panel is driven by the driving methoddescribed in the aforesaid Japanese Unexamined Patent Publication(Kokai) No. 4-362990/1992.

FIG. 1 illustrates the driving waveforms concerning pixels of interestand further illustrates change in the optical transmittance in the caseof the first embodiment of the present invention. Here, let tw1 and tw2denote a first half and a second half of the selection period tw,respectively. In the case of this embodiment, the voltage levels of thescanning signal and the display signals in the time periods tw1 and tw2,the holding period tk and the relaxation period ts in the first flameF1, are as listed hereinbelow.

    ______________________________________                                        Time Period        tw1    tw2      tk   ts                                    ______________________________________                                        Scanning Signal Voltage                                                                          0      +V1      +V3  0                                     On-State Display Signal Voltage                                                                  +V2    -V2      *    *                                     Off-State Display Signal Voltage                                                                 -V2    +V2      *    *                                     ______________________________________                                    

Additionally, the voltage levels of the display signals are set in sucha manner that |V2|>|As| and |V3+V2|<|Ft|.

In the case of the aforesaid embodiment, the values of the voltages areset as follows: V1=23.5 V, V2=6.5 V and V3=7.2 V.

The voltage (v1+V2) applied to the selection period tw in the firstframe of FIG. 1 causes the state of the liquid crystal, which has beenin the antiferroelectric state, to change into the (+) ferroelectricstate. Thus, the optical transmittance becomes high, so that the brightor light state of the pixel is displayed. In the holding period tk, thevoltages (V3-V2) and (V3+V2) are alternately applied. However, if|V3-V21|>|At|, the state of the pixel is kept the bright state.

Next, in the relaxation period ts, the voltages V2 and -V2 which are|V2|>|As| are alternately applied, and the state of the liquid crystalquickly changes the polarity from the (+) ferroelectric state to the (-)ferroelectric state with the change in the optical transmittance whichresponds to the applied voltage. Further, finally, the liquid crystal isstable in the antiferroelectric state. As is seen from the comparisonbetween FIG. 1 and FIG. 20, the time required for relaxing theferroelectric state to the antiferroelectric state from theferroelectric state in the case of this embodiment of FIG. 1 is shorterthan such a time in the case of the conventional device of FIG. 20.

The case, in which the dark state of the pixel is indicated (see L0), isconsidered as being self-evident. However, if the absolute value of thevoltage applied in the selection period tw, the holding period tk andthe relaxation period ts is smaller than the ferroelectric thresholdvoltage |Ft|, the antiferroelectric state is maintained as the state ofthe liquid crystal. Further, the optical transmittance remains low.Thus, the dark state of the pixel is exhibited.

As is seen from FIG. 1 illustrating the change in the opticaltransmittance L100, there are two types of response of the liquidcrystal in the relaxation period ts. Namely, a first type of a responseis that adapted to change in accordance with the change in the voltage±V2 (hereunder referred to as a "fast response". Further, the other typeof a response is an average one indicated by dashed lines (hereunderreferred to as a "slow response". Furthermore, it is considered that,actually, responses synthesized from the responses of these types areobserved. Additionally, judging from the comparison between the opticaltransmittances L100 respectively illustrated in FIGS. 1 and 20, it isinterpreted that the present invention speeds up the slow response.

FIG. 2 illustrates the driving waveforms concerning pixels of interestand further illustrates change in the optical transmittance in the caseof the second embodiment of the present invention. In the case of thisembodiment, another time period (hereinafter, a forced relaxation periodtr) is provided in the aforesaid relaxation period ts with the intentionof further speeding up the slow response. Moreover, in the forcedrelaxation period tr, the scanning signal voltage is set at the voltageV4 or (-V4), which has the polarity opposite to that of a scanningsignal voltage set in the preceding holding period tk. In this case, thevoltages V4 and V2 are set in the range where |As|<|V4+V2|<|Ft|.

In the case of the embodiment described hereinabove, the voltages areset as follows: V1=22 V, V2=5 V, V3=7.2 V and V4=7 V.

Here, let tw1, tw2 and ts' denote a first half and a second half of theselection period tw and a part of the relaxation period ts, which isother than the forced relaxation period tr, respectively. In the case ofthis embodiment, the voltage levels, which are represented by thescanning signal and the display signals in the first frame F1, are aslisted hereinbelow.

    ______________________________________                                        Time Period     tw1     tw2    tk    tr   ts'                                 ______________________________________                                        Scanning Signal Voltage                                                                       0       +V1    +V3   -V4  0                                   On-State Display Signal Voltage                                                               +V2     -V2    *     *    *                                   Off-State Display Signal Voltage                                                              -V2     +V2    *     *                                        ______________________________________                                    

Although the length of the forced relaxation period tr may be regulatedcontinuously, the period tr should contain at least the time periods tw1and tw2 corresponding to other rows (namely, tr≧tw1+tw2), in view of theinstability of the display data. Furthermore, considering the simplicityof the drive circuit, it is preferable that the length of the period tris an integral multiple of one horizontal scanning interval (namely,equal to the selection period tw), namely, tr=n·tw (incidentally, n is apositive integer). FIG. 2 illustrates the case where n=2.

First, the voltage (V1+V2) applied during the selection period tw in thefirst frame of FIG. 2 causes the state of the liquid crystal, which hasbeen in the antiferroelectric state, to change into the (+)ferroelectric state. Thus, the optical transmittance becomes high, sothat the bright state of the pixel of interest is shown. In the holdingperiod tk, the voltages (V3-V2) or (V3+V2) are alternately applied.However, if the absolute values of these voltages are larger than theantiferroelectric threshold voltage |At| and are smaller than theferroelectric threshold voltage |Ft|, the ferroelectric state of theliquid crystal is maintained. Thus, the optical transmittance thereofremains high. Consequently, the bright state of the pixel of interest isexhibited.

Next, when the voltages -(V4+V2) and (V4-V2) are alternately applied inthe forced relaxation period tr, the state of the liquid crystal steeplystarts changing the polarity from the (+) ferroelectric state to the (-)ferroelectric state. If the forced relaxation period tr is sufficientlylong, the change of the polarity to the (-) ferroelectric state iscompleted. However, if the length of the forced relaxation period tr andthe value of the voltage |V4| are set suitably, the change of thepolarity to the ferroelectric state in the forced relaxation period tsis interrupted. Thereby, the liquid crystal is nearly in theantiferroelectric state, though the crystal is not completely in such astate. Thereafter, the voltages +V2 and (-V2) are alternately applied,so that the liquid crystal becomes stable in the antiferroelectricstate. In accordance with this embodiment, the time required to relaxthe ferroelectric state of the liquid crystal to the antiferroelectricstate thereof is reduced in comparison with the embodiment of FIG. 1.

Although FIG. 2 illustrates the case where |V4|<|V3|, these voltages maybe set in such a way that |V4|>|V3|. Further, the voltages V2 may be setin such a manner that the following condition is satisfied: |V2|<|As|,because the aforementioned condition is satisfied: |As|<|V4+V2|<|Ft|.However, it is preferable that the voltages V2 and As are set in such away that the following condition is satisfied: |V2|>|As|.

FIG. 3 illustrates the driving waveforms of signals concerning pixels ofinterest and further illustrates change in the optical transmittance inthe case of the third embodiment of the present invention. Thisembodiment is obtained by setting the voltage V3 and V4 of the secondembodiment in such a manner that V4=V3. In this case, the number ofnecessary power supplies is reduced.

In the case of the third embodiment, the voltages are set as follows:V1=22 V, V2=5 V and V3=7.2 V and tw1, tw2 denote a first half and asecond half of the selection period tw. In the case of FIG. 3(a), inthis embodiment, the voltage levels represented by the scanning signaland the display signals in the time periods tw1 and tw2, the holdingperiod tk, the forced relaxation period tr and the relaxation periodts', which is other than the time period tr, of the first frame F1 areas listed hereinbelow.

    ______________________________________                                        Time Period     tw1     tw2    tk    tr   ts'                                 ______________________________________                                        Scanning Signal Voltage                                                                       0       +V1    +V3   -V3  0                                   On-State Display Signal Voltage                                                               +V2     -V2    *     *    *                                   Off-State Display Signal Voltaqe                                                              -V2     +V2    *     *    *                                   ______________________________________                                    

In the case of FIG. 3(b), if tw1, tw2 denote a first half and a secondhalf of the selection period tw, respectively, in this embodiment, thevoltage levels represented by the scanning signal and the displaysignals in the time periods tw1 and tw2, the holding period tk, theforced relaxation period tr and the relaxation period ts', which isother than the time period tr, of the first frame F1 are as listedhereinbelow.

    ______________________________________                                        Time Period     tw1     tw2    tk    tr   ts'                                 ______________________________________                                        Scanning Signal Voltage                                                                       +V1     +V3    +V3   -V3  0                                   On-State Display Signal Voltage                                                               -V2     +V2    *     *    *                                   Off-State Display Signal Voltage                                                              +V2     -V2    *     *    *                                   ______________________________________                                    

In this case, the number of necessary power supplies is decreased.

In the case of the embodiment of FIG. 2 or FIG. 3, the forced relaxationperiod tr is provided in such a manner as to be adjacent to the holdingperiod tk. However, a time period, in which the scanning signal voltageis zero, may be provided between the forced relaxation period tr and theholding period tk.

Viewing the optical transmittance L100 in FIG. 2 or FIG. 3, that of thecase of the slow response rises again after the elapse of the forcedrelaxation period tr, and thereafter drops as indicated by the dashedlines. It is understood that this phenomenon occurs owing to thevibration or swing of the liquid crystal molecules.

Namely, when forces are exerted on the liquid crystal molecules in theforced relaxation period tr, the molecules move in the polarityinverting direction. However, when the forces are released therefrom,the molecules once swing back toward the initial positions thereof.Thereafter, the liquid crystal becomes stable in the antiferroelectricstate.

If the motion of the molecule due to this swinging-back operation can bedamped, it is expected that the time period required to relax theferroelectric state to the antiferroelectric state is further reduced.In this case, there are tw0 cases concerning the swinging-back motion ofthe molecule. In a first case, the molecules start the movement towardthe polarity inverting direction but the movement is completed beforethe molecules reach a polarity inverting region (namely, before themolecule go through the neutral state). In the other case, the movementor motion of the molecule is completed after the molecule once passesthrough the neutral state and reaches the antiferroelectric state in theinverting region.

FIG. 4 illustrates the driving waveforms of signals concerning pixels ofinterest and further illustrates change in the optical transmittance inthe case of the fourth embodiment of the present invention based on theaforementioned idea. Namely, this embodiment corresponds to the formerone of the tw0 cases of the swinging-back motion.

This embodiment is obtained by providing a damping relaxation period tuposterior to the forced relaxation period tr in the second embodiment ofFIG. 2 and by making the scanning signal voltage in the dampingrelaxation period tu in such a manner as to be in common with thevoltage (-V5) which is different from the voltage thereof in the forcedrelaxation period tr. Although the length of the damping relaxationperiod tu may be regulated continuously, preferably, the length thereofis m·tw (incidentally, "m" is a positive integer) for the same reasonwhich has been described concerning the forced relaxation period tr.FIG. 4 illustrates the case where m=1.

In the case of the this embodiment, the voltages are set as follows:V1=22 V, V2=5 V, V3=7.2 V, V4=7 V and V5=1 V.

In this embodiment, if ts' denotes a part of the relaxation period ts,which part is other than the forced relaxation period tr and the dampingrelaxation period tu, the voltage levels represented by the scanningsignal and the display signals in the respective time periods of thefirst frame F1 are as listed hereinbelow.

    ______________________________________                                        Time Period     tw1    tw2    tk   tr   tu   ts'                              ______________________________________                                        Scanning Signal Voltage                                                                       0      +V1    +V3  -V4  -V5  0                                On-State Display Signal Voltage                                                               +V2    -V2    *    *    *    *                                Off-State Display Signal Voltage                                                              -V2    +V2    *    *    *    *                                ______________________________________                                    

In this embodiment, operations in the selection period tw and theholding period tk are similar to those in the case of the secondembodiment of FIG. 2. The liquid crystal is almost in the neutral statenearly at the termination of the forced relaxation period tr.Subsequently, after the aforementioned swinging-back movement isstarted, the force damping the swinging-back movement is given to theliquid crystal in the damping relaxation period tu. Thereby, the liquidcrystal is rapidly stabilized into the neutral state.

In the embodiment illustrated by FIG. 4, in the case that theswinging-back motion is the latter of the two cases, the scanning signalvoltage in the damping relaxation period tu may be a voltage, whosepolarity is opposite to that of the scanning voltage in the forcedrelaxation period tr, as indicated by dashed lines correspondingly to Paof FIG. 4.

In the case of the embodiment illustrated in FIG. 4, there has beendescribed the case where the forced relaxation period tr is provided insuch a manner as to be adjacent to the damping relaxation period tu.However, the forced relaxation period tr and the damping relaxationperiod tu may be provided by interposing an interval therebetween.Further, in FIG. 4, the voltages are illustrated in such a way that|V4|>|V5|. However, by suitably setting the lengths of the time periodstr and tu and the polarity of the applied voltage, these voltages may beset in such a manner that |V4|≦|V5|. Further, a plurality of the dampingrelaxation periods tu may be provided. In this case, the value of "m"and that of the voltage |V5| may be set independently of each other.

In the case of some combinations of these values, the followingconditions may hold: |V4+V2|<|As| and |V5+V2|>|As|. However, thesevalues are set so that at least one of the values |V4+V2| or |V5+V2| islarger than |As|.

Incidentally, in the case of the fourth embodiment or of the extensionthereof, as in the case of the third embodiment, one of the scanningsignal voltage in the forced relaxation period tr and the scanningsignal voltage in the damping relaxation period tu may be in common withthe scanning signal voltage in the holding period tk and may be suppliedfrom the same power source.

As above described, in the case of the hereinabove-mentioned, thepresent invention is applied to the antiferroelectric liquid crystalpanel which requires the relaxation period ts of 18 ms in the case thatthe panel is driven by the driving method (see FIG. 20) described in theaforesaid Japanese Unexamined Patent Publication (Kokai) No.4-362990/1992. For example, in the case of the second example of FIG. 2,the relaxation period ts is considerably reduced to 1.8 sec. Moreover,in the case of the device provided with the three damping relaxationtime periods tu as the extension of the fourth embodiment, therelaxation period ts is substantially reduced to 1.6 msec.

Needless to say, in the case of using other antiferroelectric liquidcrystal display panel, the aforementioned voltages V1, V2, V3, V4 and V5and the lengths of the time periods tr and tu should be set optimally.

FIG. 5 illustrates the fifth embodiment of the present invention, whichis obtained by performing a gray shade display by pulse width modulationin the third embodiment illustrated by FIG. 3. FIG. 5 illustrates thedriving waveforms and the optical transmittances in the case of shiftingthe phase of a display signal by 50%. As can be seen from this figure,the change in the optical transmittance in the relaxation period ts inthe case of this embodiment exhibits the intermediate characteristicsbetween the transmittances L100 and L0 of FIG. 3.

In the case of this embodiment, the voltages are set as follows: V1=22V, V2=5 V and V3=7.2 V.

The gray shades display by utilizing the pulse width modulation may beapplied to the first to fourth embodiments.

Meanwhile, the case of performing the gray shades display by controllingthe amplitude of a display signal will be described hereinbelow. Forinstance, in the case that only pixels selected by the scanning signalPa are in an on-state and the other pixels are in an off-state in thefirst embodiment of FIG. 1, the voltage level represented by the displaysignal Pb in the relaxation period ts is smaller than the value of |V2|.However, even in such a case, if the voltage applied to the liquidcrystal is larger than |As| of FIG. 16, the advantages or effects of thepresent invention are obtained, though the length of the relaxationperiod ts should be set in such a way as to be long to some extent. Thisis the same with the forced relaxation period tr of the second to fourthembodiments.

FIG. 6 illustrates the sixth embodiment of the present invention, whichis an extreme example of performing a gray shades display by controllingthe amplitude in the second embodiment. Further, FIG. 6 illustrates thedriving waveforms and the optical transmittances L100 in the case whenthe display signal voltage is zero in the time periods other than theselection period tw in the second embodiment. As described above, it isfound that if the voltage |V4| to be applied to the liquid crystal inthe forced relaxation period tr is larger than |As|, the advantages oreffects of the present invention are obtained. In this case, the timeperiod required to change the state of the liquid crystal from theferroelectric state to the antiferroelectric state and stabilize theliquid crystal in the latter state is 2.6 msec.

In the case of this embodiment, the voltages are set as follows: V1=22V, V2=5 V, V3=7.2 V and V4=7 V.

FIG. 7 illustrates the seventh embodiment and the case of applying thesecond embodiment (see FIG. 2) to the driving method described inJapanese Unexamined Patent Publication (Kokai) No. 6-214215/1994 (seeFIG. 19).

In this embodiment, the voltage levels represented by the scanningsignal and the display signals in the respective time periods of thefirst frame F1 are as listed hereinbelow.

    ______________________________________                                        Time Periods    tw0    tw1    tw2  tk   tr   ts'                              ______________________________________                                        Scanning Signal Voltage                                                                       0      0      +V1  +V3  -V4  0                                On-State Display Signal Voltage                                                               0      +V2    -V2  *    *    *                                Off-State Display Signal Voltage                                                              0      -V2    +V2  *    *    *                                ______________________________________                                    

In the case of the embodiment illustrated by FIG. 7, the purpose ofproviding the time period tw0 is different from that in the case of thedriving method described in Japanese Unexamined Patent Publication(Kokai) No. 6-214215/1994. Namely, in the case of the driving methoddescribed in Japanese Unexamined Patent Publication (Kokai) No.6-214215/1994, the time period tw0 is a period for the relaxation of theliquid crystal, whereas the embodiment illustrated by FIG. 7 utilizesthis period tw0 for further stabilizing the liquid crystal, which hasbeen already relaxed in the relaxation period ts, before the periods tw1and tw2. If the liquid crystal is stabilized during this period tw0, theselection operation performed in the subsequent periods tw1 and tw2completely depends on the display data. This is advantageous in the caseof performing the gray shades display.

However, the movement of the liquid crystal in the period tw1 of FIG. 7is sometimes rather wasteful. Namely, if the liquid crystal isstabilized in the period tw0, applying the voltage of (-V2) thereto inthe period tw1 results in disturbing the stabilized state thereof.

FIG. 8 illustrates the eighth embodiment of the present inventionobtained by being improved on the basis of the aforementioned idea. Thevoltage levels represented by the scanning signal and the displaysignals in the respective time periods of the first frame F1 are aslisted hereinbelow.

    ______________________________________                                        Time Periods    tw0    tw1    tw2  tk   tr   ts'                              ______________________________________                                        Scanning Signal Voltage                                                                       0      +V1    +V3  +V3  -V4  0                                On-State Display Signal Voltage                                                               0      -V2    +V2  *    *    *                                Off-State Display Signal Voltage                                                              0      +V2    -V2  *    *    *                                ______________________________________                                    

Thereby, the movement of the liquid crystal molecule starts from thestate stabilized in the period tw0. Thus, the selection voltage isapplied thereto in the time period tw1. Consequently, a stable displayof each pixel is possible even in the case of performing a delicate grayshades display.

FIG. 9 is a diagram showing the driving waveforms and the opticaltransmittances in the case of the device of the present invention, whichillustrates the influence of temperature thereon. In this figure, L(H)designates the optical transmittance in the case where the ambienttemperature (40 degrees centigrade) of the second embodiment illustratedby FIG. 2 is made to be higher than the room temperature; L(N)designates the optical transmittance in the case where the ambienttemperature is equal to the room temperature; and L(L) designates theoptical transmittance in the case where the ambient temperature (15degrees centigrade) of the second embodiment illustrated by FIG. 2 ismade to be lower than the room temperature.

The characteristics of the antiferroelectric liquid crystal panel varywith temperature. Investigation has revealed that, especially, theaforementioned slow response heavily depends on the temperature.Therefore, in the case that the ambient temperature changes during thedriving conditions in the forced relaxation period tr are fixed, whenthe ambient temperature changes to a high temperature, the movement ofthe liquid crystal molecules in the forced relaxation period tr becomesexcessive as illustrated in FIG. 9. In contrast, when the ambienttemperature changes to a low temperature, the movement of the liquidcrystal molecules in the forced relaxation period tr becomesinsufficient. Consequently, the value of the voltage applied to theliquid crystal in the forced relaxation time period tr and that of thelength of this time period are shifted from the optimum values. Thus,the time required to relax the state of the liquid crystal tends toincrease. This is the same with the damping relaxation period tu in thecase of the fourth embodiment of FIG. 4. Namely, the applied voltage inthe damping relaxation period tu does not serve as the damper for theslow response. Conversely, the applied voltage sometimes acts in such away as to increase the movement of the molecule. Although it isconsidered that temperature compensation is performed on the values ofthe voltages V1, V2 and V3 in this case, these values relates to theoperations performed in the selection period tw and the holding periodtk. Thus, the temperature compensation is permitted only in the rangewhere the operations in these time periods are ensured, therefore, itcannot be made to change the above value of the voltages withoutlimitation. Moreover, the voltages V1 and V3 basically have small effecton the relaxation operation (except the case that ±V4 and ±V3 are madeto be in common with each other in the forced relaxation period tr).Hence, the temperature compensation is sometimes insufficient forcompensating for the operation performed in the relaxation period ts.

FIG. 10 is a waveform diagram illustrating the waveforms of scanningsignals used in the ninth embodiment of the present invention, which isused for solving the problem described hereinabove. This figureillustrates the case of applying this embodiment to the aforementionedfourth embodiment. FIG. 10(a) illustrates the case where the scanningsignal voltage (-V4) or V4 is changed depending on temperature in theforced relaxation period tr. For example, in the first frame, when thetemperature is high, the voltage level of (-V4) is raised. In contrast,when the temperature is low, the voltage level of (-V4) is dropped. Thecompensation is performed in this manner, so that the movement of theliquid crystal molecules in the forced relaxation period tr is preventedfrom becoming excessive when the temperature is high, or from becominginsufficient when the temperature is low.

FIG. 10(b) illustrates the case where both of the scanning signalvoltage |V4| in the forced relaxation period tr and the scanning signalvoltage |V5| in the damping relaxation period tu are changed in such amanner as to depend on the temperature.

FIG. 10(c) illustrates the case where only the scanning signal voltage|V5| in the damping or decelerating relaxation period tu is changed insuch a way as to depend on temperature.

Needless to say, as illustrated in FIG. 10(c), the voltages |V1| and|V3| may be changed in such a way as to depend on the temperature. Thisis the same with the voltage |V2|. Further, the values of "m" and "n"may be changed (incidentally, the switching therebetween is included)according to the temperature, in conjunction with the temperaturecompensation of or instead of the voltage levels.

FIG. 11 includes a block diagram showing the configuration of a circuitfor implementing the ninth embodiment of the present invention and acharacteristic diagram illustrating the manner of the temperaturecompensation. In FIG. 11(a), row electrodes, to which scanning signalsof the antiferroelectric liquid crystal panel 1 are applied, areconnected to a row electrode drive circuit 2. Further, columnelectrodes, to which display signals are applied, are connected to acolumn electrode circuit 3. The voltages ±V1, ±V3, ±V4 and ±V5 requiredto drive the row electrodes of the liquid crystal panel are suppliedfrom a power supply circuit 4 to the row electrode drive circuit 2,together with a voltage being necessary for operating the row electrodedrive circuit 2. The voltages ±V2 required to drive the columnelectrodes of the liquid crystal panel are supplied from the powersupply circuit 4 to the column electrode drive circuit 3, together witha voltage being necessary for operating the column electrode drivecircuit 3.

Control circuit 5 is operative to supply signals to the row electrodedrive circuit 2 and the column electrode drive circuit 3 according toinformation sent from a display data generating source 7. The rowelectrode drive circuit 2 and the column electrode drive circuit 3supply, based on the given signals, scanning signals, whose signal levelconsists of the voltages ±V1, ±V3, ±V4 and ±V5, and display signals,whose signal level consists of the voltages ±V2, to the liquid crystalpanel 1.

Temperature compensation means 6 is operative to detect the temperatureof the liquid crystal panel 1 and that in the vicinity thereof and tocause at least one or both of ±V4 and ±V5 to change according to aresult of the detection, among ±V1, ±V2, ±V3, ±V4 and ±V5. As statedabove, the temperature compensation means 6 may be connected to thecontrol circuit 5 to thereby change the values of "m" and "n" accordingto the temperature. FIGS. 11(b) to 11(e) illustrate the typical examplesof the cases where the scanning signal voltages are caused by thetemperature compensation means 6 to change depending on the temperaturein the device of the FIG. 11(a). FIG. 11(b) illustrates an example ofthe case that the temperature compensation is performed only on thescanning signal voltage ±V4 in the forced relaxation period tr, asillustrated in FIG. 10(a). In this case, the voltages ±V5 are maintainedat constant values, respectively, independent of the temperature. Thevoltage V4 is lowered with an increase in the temperature, while thevoltage (-V4) is raised with increase in the temperature. In some case,V4 is negative and (-V4) is positive.

FIGS. 11(c) and 11(d) illustrate an example of the case that thetemperature compensation is performed on both of the scanning signalvoltage ±V4 in the forced relaxation period tr and the scanning signalvoltage ±V5 in the damping relaxation period tu, as illustrated by FIG.10(b). Incidentally, as is apparent from FIG. 10(b), V4 and (-V4) aredifferent from each other only in the reverse polarity. This is the samewith the relation between V5 and (-V5). Hereinafter, for simplicity ofdescription, the description will be made only concerning (-V4) and(-V5), with reference to the drawings.

In this case, as illustrated in FIG. 11(c), both of the voltage levelsof (-V4) and (-V5) may be raised with the rise of the temperature.Alternatively, with the rise of the temperature, the voltage level of(-V4) may be raised, while the voltage level of (-V5) may be dropped asillustrated in FIG. 11(d). In some case, (-V4) becomes positive, or(-V5) becomes positive.

FIG. 11(e) illustrates an example of the case that the temperaturecompensation is performed only on the scanning signal voltage ±V5 in thedamping relaxation period tu, as illustrated in FIG. 10(c). In thiscase, the voltage (-V5) is raised with the rise of the temperature,while the voltages ±V4 are maintained at constant values, respectively,independent of the temperature. In some cases, (-V5) is positive.

The characteristics illustrated in the diagrams of FIGS. 11(b) and 11(c)are not fixed. When using a liquid crystal panel of differentcharacteristics, or when changing the lengths of the forced relaxationperiod tr and the damping relaxation period tu, the optimum values ofthe voltages corresponding to the temperatures vary in response to sucha change. Thus, it is natural that the values of the individual voltages(-V4) and (-V5) and the relation therebetween are different from thoseof FIG. 11. Furthermore, the optimum values of ±V4 and ±V5 may vary withthe values of the voltages ±V1, ±V2 and ±V3, especially, with the valuesof ±V2. Therefore, a change in the optimal temperature characteristicsof ±V4 and ±V5 is caused depending on the manner of the temperaturecompensation performed on the voltages ±V1, ±V2 and ±V3.

The examples of the temperature compensation illustrated in FIG. 10 or11 have been described in the case of the fourth embodiment of FIG. 4,namely, in the case of the device provided with both of the forcedrelaxation period tr and the damping relaxation period tu. However,needless to say, the example of the temperature compensation performedonly on the forced relaxation period tr as illustrated in FIG. 10(a) or11(b) may be applied to the case where the device is not provided withthe damping relaxation period tu.

Meanwhile, the scanning signal voltage ±V4 in the forced relaxationperiod tr in the case of the second or fourth embodiment, or thescanning signal voltage ±V5 in the damping relaxation period tu in thecase of the fourth embodiment may be in common with the scanning signalvoltage ±V3 in the holding period tk. Moreover, the power supply may beused in common, as above described. In such a case, regarding the fourthembodiment, at least one of ±V4 and ±V5 is not in common with ±V3. Thus,by applying one of the temperature compensation methods of FIGS. 10(a)to 10(c) and 11(b) to 11(e) to this voltage (set), which are not commonwith ±V3, the temperature compensation suited to the relaxationoperation can be performed. However, the second embodiment is notprovided with the damping relaxation period. Thus, if the scanningsignal voltages ±V4 and ±V3 in the forced relaxation period tr are madeto be in common with each other, the temperature compensation suited tothe relaxation is not necessarily achieved. Hence, in some cases, thetime required to perform the relaxation is abnormally long. Thus, thereis a fear that the device cannot operate.

FIG. 12 is a diagram illustrating the driving waveforms and a change inthe optical transmittance in the case of the tenth embodiment of thepresent invention. In the case of this embodiment, in the relaxationperiod ts, the scanning signal voltage is alternately changed between(-V4) and V4 every time period te. FIG. 12 illustrates the case thatte=3·tw (incidentally, tw is the length of the selection period, namely,one horizontal scanning interval). In this case, the voltages are set insuch a way that the following condition is satisfied: |V4+V2|>|As|.

In the case of this embodiment, the voltages are set as follows: V1=22V, V2=5 V, V3=7.2 V and V4=7 V.

L(H), L(N) and L(L) of FIG. 12 designate the changes in the opticaltransmittance, which respectively correspond to the cases that thetemperature of the same liquid crystal panel is high, that thetemperature thereof is room temperature and that the temperature thereofis low. In the case of L(N), the time required to relax is long. Incontrast, in the case of L(H) and L(L), the relaxation time is short, incomparison with that of the case of FIG. 9. Moreover, as a whole, thetemperature dependency of the relaxation period ts becomes small. In thecase of FIG. 12, the relaxation period ts is about 3.3 msec at alltemperatures. This is long, as compared with the relaxation period,which is 1.8 msec, of the second embodiment of FIG. 2. However, notethat a time period of 18 msec is needed by the device, which is notaccording to the present invention, even at room temperature. It is,therefore, clear that extremely profound advantages are obtained.

Incidentally, in the case of L(N) of FIG. 12, thin solid curves indicateresults obtained by the tenth embodiment on the same display conditions(namely, in the time periods other than the selection period tw, |V2|=0)as of FIG. 6. According to the results, in the case of the tenthembodiment, if the values of ±V4 are suitable, the relaxation process inthe relaxation period ts can be regarded as having caused almost nochange, even if the values of ±V2 change considerably.

Further, even in the case where the device is set in such a manner thatte=4·tw, the results are almost the same as of the case that te=3·tw, asa whole. Namely, in the case of the tenth embodiment of FIG. 10, therelaxation period ts has relatively small dependence on the temperature,the value of te and the value of the applied voltage.

In the case of the embodiment of FIG. 12, the relaxation period shouldbe set to be somewhat long. However, the range of tolerance on theambient temperature, the value of the scanning signal voltage ±V4 duringthe relaxation period ts and the length of the time period te is wide.Even when sufficient effects of the temperature compensation are notobtained for the aforementioned reason by setting ±V4 in such a manneras to be in common with ±V3, the range of the condition in which thedevice normally operates can be widened Needless to say, the temperaturecompensation may be performed on ±V4 independently. Further, in the caseof the embodiment of FIG. 12, the scanning signal voltage is alternatelychanged between ±V4 and (-V4) over the entire relaxation period ts everyperiod te. However, this change of the polarity may be performed only ina part of the relaxation period ts, and the reference voltage may beapplied in the rest of the relaxation period. Alternatively, in the restof the relaxation period, the applied voltage may be changed between thevoltages ±V5 and (-V5), whose absolute values are different from thoseof ±V4. In this case, the temperature compensation may be performed onat least one of |V4| and |V5|.

In the case of the embodiment of FIG. 12, it is uncertain whether eachperiod te in the relaxation period ts serves to accelerate or deceleratethe motion of the liquid crystal. Probably, the acceleration and thedeceleration act on the motion of the liquid crystal molecule indisorder. Further, it is considered that the state of the moleculefinally comes close to the no-voltage neutral state. In this case, whenthe period te has some length, the time period required to perform therelaxation may be extremely long owing to the resonance phenomenonbetween the period or cycle of the motion of the molecule and the periodte. In such a case, the time period te may vary regularly orirregularly. Similarly, the time period te may be adapted to changedepending upon temperature.

Furthermore, in the case of the embodiment of FIG. 12, the polarity ofthe scanning signal voltage applied in a first time period te in therelaxation period ts is not necessarily opposite to that of the voltageapplied in the holding period tk which immediately precedes the firsttime period te. The beginning or end of the time period te must notcoincide with the beginning or end of the relaxation time ts.

FIG. 13 is a diagram illustrating the driving waveforms in the cases ofthe eleventh and the twelfth embodiments of the present invention basedon such an idea. In FIG. 13, P1, P2, P3 and P4 designate the waveformsof scanning signals applied to adjacent four row electrodes. Further, Vxdenotes an alternating (variation) voltage, whose value is alternatelychanged between V4 and (-V4) every time period te.

In FIG. 13, the scanning signal voltages applied in the time period tw1,which are indicated by the thin solid lines, respectively, correspond tothe eleventh embodiment. Further, the scanning signal voltages appliedin the time period tw1, which are indicated by the thick dashed lines,respectively, correspond to the twelfth embodiment.

First, let tw1 and tw2 denote a first half and a second half of theselection period tw, respectively, in the case of this embodiment. Thevoltage levels, which are represented by the scanning signal and thedisplay signals in the period tw1, tw2, the holding period tk and therelaxation period ts of the first frame F1 are as listed hereinbelow.

    ______________________________________                                        Time Period      tw1    tw2      tk   ts                                      ______________________________________                                        Scanning Signal Voltage                                                                        0      +V1      +V3  Vx                                      On-State Display Signal Voltage                                                                +V2    -V2      *    *                                       Off-State Display Signal Voltage                                                               -V2    +V2      *    *                                       ______________________________________                                    

The variation voltage Vx is independent of the scanning of each of therow electrodes. Relative changes in the scanning signal voltages in therelaxation periods ts respectively corresponding to the row electrodesP1, P2, P3 and P4 are different from one another. Namely, a leadingscanning signal voltage in the relaxation period ts is, in a certaintime, (-V4) (in the case of the row electrodes P1, P2 and P3) but is, inanother time, ±V4 (in the case of the row electrode P4). Moreover, thetime required to invert the polarity of the voltage is not uniform.Therefore, there is a variation among the motions of the liquid crystalmolecules in a leading portion of the relaxation period ts correspondingto the row electrodes, respectively. However, thence, the alternation ofthe scanning signal voltage is repeatedly performed. In the meantime,the relaxation of the liquid crystal on each of the row electrodes isachieved. Finally, the liquid crystals are brought into even or uniformantiferroelectric states, respectively.

In the case of the embodiment of FIG. 12, the scanning signal voltage ischanged among 0, ±V1, ±V2, ±V3 and ±V4 in the relaxation period ts.Therefore, this embodiment needs a switch that has seven contact points.Differently from this, the eleventh embodiment of FIG. 13 has only tohave a six-contact switch for switching the voltage among 0, ±V1, ±V3and Vx. Output-voltage changing switch should be provided at each outputterminal in the drive circuit. Moreover, relatively large currents flowthrough the antiferroelectric liquid crystal panel. Thus, the internalresistance of these switches used in the drive circuit should besufficiently low.

In the case where the drive circuit is formed as an integrated circuitwhich uses a field effect transistor (hereunder abbreviated as FET), theswitch should have a fairly large size so as to provide a low internalresistance. This results in considerable reduction in the efficiency inintegration. Therefore, the reduction in the number of necessaryswitches has an advantage in considerable decrease in size of theintegrated drive circuit. Consequently, the present invention hasprofound economic merits.

In this respect, the eleventh embodiment of FIG. 13 is advantageous overthe tenth embodiment of FIG. 12.

Next, in the case of the twelfth embodiment, assuming that the scanningsignal voltages are indicated by dashed lines in FIG. 13, the voltagelevels, which are represented by the scanning signal and the displaysignals in the first frame are as listed hereinbelow.

    ______________________________________                                        Time Period      tw1    tw2      tk   ts                                      ______________________________________                                        Scanning Signal Voltage                                                                        Vx     +V1      +V3  Vx                                      On-State Display Signal Voltage                                                                +V2    -V2      *    *                                       Off-State Display Signal Voltage                                                               -V2    +V2      *    *                                       ______________________________________                                    

In this case, the operation performed in the relaxation period ts issimilar to that in the case of the eleventh embodiment but is differentfrom each other only in the voltage applied in the first time period tw1of the selection period tw. In the case of the twelfth embodiment, in aceratin time, the scanning signal voltage in the period tw1 is (-V4)(namely, corresponding to the electrodes P1, P2 and P3) but, in anothertime, the scanning signal voltage is ±V4 (corresponding to the electrodeP4). This difference between the scanning signal voltages may affect themotion of the liquid crystal molecule in an initial stage of the timeperiod tw2. In such a case, when effecting the gray shades display whichrequires delicately controlling the ferroelectric state or condition,problems may be caused. However, if the gray shades display is not ineffect, the display can be effected without a problem.

Further, the twelfth embodiment has only to provide a five-contactswitch, which is used for switching the voltage among ±V1, ±V3 and Vx,in the row electrode drive circuit. Thus, the twelfth embodiment isfurther advantageous over the eleventh embodiment.

FIG. 14 illustrates the thirteenth embodiment of the present invention,which is obtained by setting the voltage of the alternating voltage vxat 0 in the period corresponding to the time period tw1 of each of thescanning signals (which correspond to the electrodes P1, P2, . . . ,respectively) in the aforementioned twelfth embodiment. The displaysignals are assumed to have the same waveforms as illustrated in FIG.12. Namely, in the case of the thirteenth embodiment, the voltagelevels, which are represented by the scanning signal and the displaysignals and the alternating voltage Vx in the first frame are as listedhereinbelow. Here, the symbol "#" with respect to Vx indicates that thevoltage is one of ±V4, 0 and (-V4).

    ______________________________________                                        Time Period      tw1    tw2      tk   ts                                      ______________________________________                                        Scanning Signal Voltage                                                                        Vx     +V1      +V3  Vx                                      On-State Display Signal Voltage                                                                -V2    +V2      *    *                                       Off-State Display Signal Voltage                                                               +V2    -V2      *    *                                       Vx               0      #        #    #                                       ______________________________________                                    

In FIG. 14, the voltage represented by each of the scanning signals isthe alternating (variation) voltage Vx in the time period tw1. Further,the alternating voltage Vx is 0, so that the scanning signal voltage is0 in the time period. Thus, the voltage applied to the liquid crystal inthis time period is defined uniquely according to the voltage applied tothe liquid crystal in the time period tw2. The motion of the liquidcrystal molecular in this time period is constant correspondingly to thedisplay data. Therefore, no problems are caused in the gray shadesdisplay.

Thereafter, the scanning signal voltage is ±V1 in the time period tw2,and is ±V3 in the holding period tk, and is again changed into thevariation voltage Vx in the relaxation period ts.

In the relaxation period ts, a time period, in which the scanning signalvoltage is changed between 0 and ±V4, and another time period, in whichthe scanning signal voltage is changed between 0 and (-V4), arealternately and continuously provided. In this case, the voltage appliedto the liquid crystal is ±V2, ±(V4+V2) or ±(V4-V2) in accordance withthe display data. However, in the case of some display data, the appliedvoltage is fixed to ±V2 and ±(V4+V2), or ±V2 and ±(V4-V2). However, asdescribed regarding the case as indicated by thin solid lines in thedescription of FIG. 12, if the maximum value of the voltage, whosepolarity is alternately changed, applied to the liquid crystal, is morethan a certain value, almost same relaxation operations are performedeven if the valve of voltage changes. If any inconvenience occurs inconjunction with this respect, the fourteenth embodiment, which will bedescribed hereinbelow, is effective in such a case.

FIG. 15 is a diagram illustrating the waveforms of the scanning signalsin the case of the fourteenth embodiment of the present invention. Thefourteenth embodiment is adapted so that the maximum voltage in therelaxation period ts is ±(V4+V2) independent of display data at least inthe case when the gray shades display utilizing the amplitude control isnot performed. In the case of this embodiment, similarly as in the caseof the embodiment of FIGS. 7 and 8, the selection period tw is dividedinto three time periods tw0, tw1 and tw2 (incidentally, tw1=tw2). Thescanning signal voltage is ±V1 in the time period tw1, and is ±V3 in thetime period tw2 and the holding period tk, and is Vx in the relaxationperiod ts and the time period tw0. Further, the alternating voltage Vxis 0 only in the time period corresponding to the time period tw0 ofeach of the scanning signals. The waveforms of display signals areassumed to be similar to those of FIG. 8. Namely, in the case of thefourteenth embodiment, the voltage levels, which are represented by thescanning signal, the display signals and the alternating (variation)voltage Vx in each of the time periods in the first frame are as listedhereinbelow.

    ______________________________________                                        Time Period     tw0    tw1    tw2   tk   ts                                   ______________________________________                                        Scanning Signal Voltage                                                                       Vx     +V1    +V3   +V3  Vx                                   On-State Display Signal Voltage                                                               0      -V2    +V2   *    *                                    Off-State Display Signal Voltage                                                              0      +V2    -V2   *    *                                    Vx              0      #      #     #                                         ______________________________________                                    

In the case of this embodiment, the synthetic voltage to be applied is 0in the time period tw0. Further, the applied voltage is (v1+V2) or(V1-V2) in the time period tw1. Thus, the ferroelectric state or theantiferroelectric state is selected. Moreover, in the relaxation periodts, a time period, in which 0 and V4±V2 coexist, and another timeperiod, in which 0 and -V4±V2 coexist, are alternately and continuouslyprovided. In this case, in the periods tw1 and tw2, the scanning signalvoltage is necessarily ±V4, so that the maximum value of the voltageapplied to the liquid crystal in the relaxation period ts is necessarily±(V4+V2). Consequently, the relaxation operation in the relaxationperiod ts is made further uniform.

Furthermore, the fourteenth embodiment of FIG. 15 has the sameadvantages as of the eighth embodiment of FIG. 8. Namely, the selectionvoltage is applied in the time period tw1. Thus, the motions of theliquid crystal molecules are started from a state in which the liquidcrystal is in a stable state in the time period tw0. Thereby, thedisplay can be stably effected even in the case of performing a delicategray shades display.

In FIGS. 13 to 15, there have been illustrated the case in which thereis a certain relation between the alternating period of the alternating(variation) voltage Vx and the frame period and in which the polarity ofthe voltage is inverted every frame. However, there may be no relationbetween the alternating period of the alternating voltage Vx and theframe period. Further, the alternating period of the alternating voltageVx may be asynchronous to the frame period. In this case, the period orcycle of the alternating voltage may be controlled by an oscillator orthe like, on which the temperature compensation has been performed.Thus, the alternating period may be adapted to change into a suitablevalue. Needless to say, the temperature compensation may be performed onthe value of the alternating variation voltage Vx.

Incidentally, the scanning electrode drive circuit used for driving theconventional antiferroelectric liquid crystal panel has a five-contactswitch which is provided at each output terminal and is used forchanging the output scanning signal voltage among 0 (namely, thereference potential), ±V1 and ±V3. Moreover, the device is configured sothat the switch timing can be altered in accordance with an externalsignal.

On the other hand, in the case of the twelfth embodiment of FIG. 13, thethirteenth embodiment of FIG. 14 and the fourteenth embodiment of FIG.15, the number of necessary output switches is only five. Thus, theseembodiments are implemented without largely modifying the conventionalscanning electrode drive circuit. In the case that the scanningelectrode drive circuit has already been integrated, the device of thepresent invention has huge advantage. The inventor of the presentinvention could implement these embodiments only by changing inputsignals and supplied voltage without changing the scanning electrodedrive circuit.

Meanwhile, as is apparent from the foregoing description, the drivingmethod illustrated by FIGS. 1 and 2 of Japanese Unexamined PatentPublication (Kokai) No. 4-362990/1992 should meet the followingconditions (1) to (5).

    ______________________________________                                               |V1 - V2| < |Ft|                                           (1)                                                          |V3 + V2| < |Ft|                                           (2)                                                          |V1 + V2| > |Fs|                                           (3)                                                          |V3 - V2| > |At|                                           (4)                                                          |V2| < |As|                                                (5)                                                   ______________________________________                                    

For example, the following inequality (A) is obtained from theinequality (1) and the inequality (3). Further, the following inequality(B) is obtained from the inequality (2) and the inequality (4).Moreover, the inequality (C) is obtained by modifying the inequality(5). Thus, the conditions for constraining the driving are obtained asfollows.

    ______________________________________                                               V2 > (Fs - Ft)/2 (A)                                                          V2 < (Ft - At)/2 (B)                                                          V2 < As          (C)                                                   ______________________________________                                    

Further, it is concluded from these conditions that unless theantiferroelectric liquid crystal does not meet both of the followingconditions (a) ad (b), a sufficient display cannot be achieved by thedriving method described in FIG. 1 and FIG. 2 of Japanese UnexaminedPatent Publication (Kokai) No. 4-362990/1992.

(a) Ft-At>Fs-Ft

(b) Fs-Ft<2*As

However, it is very difficult to produce a liquid crystal panel meetingthe conditions (a) and (b) while simultaneously satisfying thespecifications (the number of rows to be displayed, the range of workingtemperature, the frame frequency and so on) required of an actualdisplay device. Especially, no liquid crystal panels, which sufficientlysatisfies the working temperature, have been realized at present.

In view of the present circumstances, it is very important to provide afurther high-performance practical display device by alleviatingconstraints necessary for driving the panel and by mitigating optionalconditions for producing a liquid crystal panel.

In this respect, Japanese Unexamined Patent Publication (Kokai) No.4-362990/1992 described that in the case that a time period, in whichthe voltage |V3 -V2| is applied, is relatively sufficiently shorter thanthe relaxation time tn, the state of a liquid crystal can be sometimesheld by setting |V3-V2|<|At| in a nonselection period (corresponding toa holding period tk). Further, Japanese Unexamined Patent Publication(Kokai) No. 4-362990/1992 describes a method of driving anantiferroelectric panel, in which |FS-Ft| is large and |V2| is set at alarge value by utilizing this property. This method, however, is notsuited to a high precision display device, because the selection periodtw should be lengthened in the case of using a liquid crystal panel, inwhich the relaxation time tn is long.

However, in the case of the first embodiment of the present invention ofFIG. 2, the value of |V2| can be made to be larger than that of |As|within the range where |V2|<|Ft|. Further, in the case of the otherembodiments, the value of |V2| can be made to be larger than that of|As| in the range where |As|<|V4+V2|<|Ft|, or in the range where|As|<|V5+V2|<|Ft|. Therefore, the constraint |V2|<|As| can beeliminated. The present invention has great advantage in providing adisplay device, which has a higher performance and is more practical, byalleviating optional conditions for producing a liquid crystal panel.

We claim:
 1. An antiferroelectric liquid crystal display device having aselection period tw and a holding period tk, and a relaxation period tsthat is time period for changing a state of a liquid crystal from aferroelectric state to an antiferroelectric state after the holdingperiod tk and before the selection period tw,wherein an absolute valueof a display signal voltage is made to be larger than an absolute valueof an antiferroelectric saturation voltage.
 2. An antiferroelectricliquid crystal display device having a selection period tw and a holdingperiod tk, and a relaxation period ts that is a time period for changinga state of a liquid crystal from a ferroelectric state to anantiferroelectric state after the holding period tk and before theselection period tw,wherein at least one non-zero horizontal scanninginterval, in which the scanning signal voltage is not zero at least in adisplay signal active period, is provided in the relaxation period ts.3. An antiferroelectric liquid crystal display device having a selectionperiod tw and a holding period tk, and a relaxation period ts that is atime period for changing a state of a liquid crystal from aferroelectric state to an antiferroelectric state after the holdingperiod tk and before the selection period tw,wherein at least tw0non-zero horizontal scanning intervals, in which the scanning signalvoltage is not zero at least in a half of a display signal active periodin one period of a display signal, is provided in the relaxation periodts.
 4. The antiferroelectric liquid crystal display device according toclaim 2 or 3, wherein both of horizontal scanning intervals areprovided, one is the horizontal scanning interval in which the non-zerohorizontal scanning interval is a positive voltage, and the other is thehorizontal scanning interval in which the non-zero horizontal scanninginterval is a negative voltage.
 5. The antiferroelectric liquid crystaldisplay device according to claim 2 or 3, wherein a positive voltage anda negative voltage is alternately applied as the scanning signal voltageto be applied in the relaxation period ts.
 6. The antiferroelectricliquid crystal display device according to claim 2 or 3, wherein thescanning signal voltage is supplied from an alternating variationvoltage source at least in a part of the relaxation period ts.
 7. Theantiferroelectric liquid crystal display device according to claim 6,wherein the voltage from the alternating variation voltage source ismade to be zero in a part of each of the horizontal scanning intervals.8. The antiferroelectric liquid crystal display device according toclaim 2 or 3, wherein the non-zero horizontal scanning interval t andthe selection period tw meet the following condition:t≧tw.
 9. Theantiferroelectric liquid crystal display device according to claim 2 or3, wherein a horizontal scanning interval period, in which the scanningsignal voltage is not zero, is an integral multiple of a period of adisplay signal.
 10. The antiferroelectric liquid crystal display deviceaccording to claim 2 or 3, wherein a time period, in which the scanningsignal voltage is zero, is provided between the holding period tk andthe non-zero horizontal scanning interval.
 11. The antiferroelectricliquid crystal display device according to claim 2 or 3, wherein a firstnon-zero scanning signal voltage in the relaxation period ts is set at anegative voltage when the state of the liquid crystal in a precedentholding period is a (+) ferroelectric state, and is set at a positivevoltage when the state of the liquid crystal in the precedent holdingperiod is a (-) ferroelectric state.
 12. The antiferroelectric liquidcrystal display device according to claim 2 or 3, wherein an absolutevalue of a scanning signal voltage in the holding period tk is made tobe equal to an absolute value of a scanning signal voltage in thenon-zero horizontal scanning interval, in at least in a part therelaxation period ts.
 13. The antiferroelectric liquid crystal displaydevice according to claim 2 or 3, wherein the antiferroelectricsaturation voltage As, a ferroelectric threshold voltage Ft, a displaysignal voltage V2 and a scanning signal voltage V4 in the non-zerohorizontal scanning interval satisfy the followingcondition:|As|<|V4+V2|<|Ft|.
 14. The antiferroelectric liquid crystaldisplay device according to claim 2 or 3, wherein the scanning signalvoltage is made to change in response to variation in temperature atleast in a part of each of the relaxation period ts.
 15. Theantiferroelectric liquid crystal display device according to claim 2 or3, wherein the scanning signal voltage is made to be a selection voltagein a first half of a display signal active period in one period of adisplay signal, and wherein the scanning signal voltage is made to beequal to a scanning signal voltage, which is established in the holdingperiod tk, in a second half of the display signal active period.